Air interfaces of communications networks have multiple RATs (radio access technologies) such as GSM (Global System for Mobile Communications), UMTS (Universal Mobile Telecommunications System), and LTE (Long Term Evolution, Long Term Evolution).
Communication between a UE (user equipment) and a network is closely related to an RAT used by an air interface of an access network. One access network of the GSM is GERAN (GSM/EDGE radio access network), one access network of the UMTS is UTRAN (UMTS terrestrial radio access network), and one access network of the LTE is E-UTRAN (evolved-UTRAN). Herein, the EDGE (enhanced data rate for GSM evolution) is an evolved technology of the GSM. The GSM is a 2G (second generation) mobile communications system, the UMTS is a 3G (third generation) mobile communications system, and the LTE is a 4G (fourth generation) mobile communications system.
L3 (Layer 3) signaling and NAS (non-access stratum) signaling in service setup, service running, and service releasing processes of a UE are all bound to the RAT of the air interface. For example, if the UE is registered with or location updated to an MSC (mobile switching center) of a GSM core network, signaling about registration/location update is all transmitted over a GSM air interface.
In this manner of binding the NAS signaling and the L3 signaling to the RAT of the air interface, the NAS signaling and the L3 signaling cannot flexibly use advantages of various air interfaces during setup of different types of services or during service running. For example, signaling cannot be flexibly transmitted according to factors such as load, leading to a long delay, low efficiency, and a high failure probability in service setup and running.